My dad has two Commander 1000s. One is good. The other just started acting up a few weeks ago. It will run for a few seconds. He has already swapped out fuel pump. I removed fuel cap to check for vapor lock. You can hear pump turn on when the key is switched. It will start up then shut right off. Then when you turn back on the fuel pump will not engage. If he let's it sit for a few minutes he can turn it on and do the same series again. Any suggestions.